The use of inhibitors of the binding interaction between uPA and uPAR provide a method for preventing or counteracting localised extracellular proteolytic activity in a mammal, in particular a human, by preventing the binding of a receptor-binding form of uPA to uPAR in the mammal and thereby reducing the ability of uPA to convert plasminogen into plasmin. This mechanism is inter alia described in N. Behrendt et al. (1995) Biol. Chem. Hoppe-Seyler, 376:269–279 and in WO 90/12091. While the binding of uPA is known to be necessary for optimal performance of cell-surface proteolysis, blocking of uPA may also have other anti-tumour effects in the context of cell signalling, cell adhesion and migration. Such alternative mechanisms are e.g. suggested in Min et al., Cancer Research, 56: 2428–2433 (1996).
Peptide inhibitors of the uPA/uPAR interaction have previously been described (see R. J. Goodson et al. (1994) Proc. Nat. Acad. Sci. U.S.A. 91:7129–7133; M. Bürgle et al. (1997) Biol. Chem. 378: 231–237; U.S. Pat. No. 5,656,726; WO 97/35969 and WO 97/24453).
Thus, Goodson et al. disclosed nineteen linear 15-mers comprising of two relatively short conserved subsequences: LWXXAr (Ar=Y, W, F or H) and XFXXYLW, neither of which are found in uPA or its receptor (uPAR). The peptides were tested in a UPAR binding assay, wherein the most potent inhibitor (the so-called “Clone 20”: AEPMPHSLNFSQYLWYT (SEQ ID NO:2)) showed an apparent inhibition constant at 10 nM for the uPAR-ATF interaction.
Bürgle, et al. studied the ability of synthetic peptides derived from the uPAR binding region of uPA (i.e. comprising the amino acids 16–32 of uPA) to inhibit the uPA/uPAR interaction. Moreover, various disulfide-bridged cyclic forms of the above-mentioned peptide were tested and it was found that the cyclo19,31uPA19-31 was a relatively potent inhibitor of the uPA/uPAR interaction.
WO 97/35969 (Chiron) describes a number of peptides capable of binding to uPAR thereby inhibiting the binding of an integrin and vitronectin.
WO 97/05257 (Chiron) relates inter alia to polypeptides and analogues thereof capable of binding to uPAR and thereby inhibit the receptor binding activity of uPA. The peptides studied all comprised the following sequence:L-(N/C)F-(G/s)-(Q/C/c)-Y-L-(W/nA)-(Y/C)-Twherein capital letters designate L-amino acids, lower case letters designate D-amino acids and nA denotes 1-naphthylalanine. It was found that inclusion of D-serine in the position next to the fixed phenylalanine in most cases caused a 2–5 fold decrease in the obtained IC50 value.